The present invention pertains to a copper alloy sputtering target which allows the formation of a seed layer being stable, uniform and free from the occurrence of coagulation during copper electroplating and which exhibits excellent sputtering film formation characteristics, the manufacturing method thereof, and a semiconductor element wiring formed with such a target.
Conventionally, Al (specific resistance of roughly 3.1 μΩ·cm) has been used as the wiring material of a semiconductor element, but copper wiring with lower resistance (specific resistance of roughly 1.7 μΩ·cm) has been put into practical application pursuant to the miniaturization of wiring.
With the current formation process of copper wiring, often times, after forming a diffusion barrier layer of Ta/TaN or the like in a contact hole or the concave portion of a wiring groove, copper is electroplated thereto. In order to perform this electroplating, as the foundation layer (seed layer), generally, copper or copper alloy is sputtered and deposited thereto.
Ordinarily, electrolytic copper having a purity of 4N (excluding gas components) is employed as the crude metal in a wet or dry high purification process to manufacture high purity copper having a purity of 5N to 6N, and this was used as the sputtering target. Here, there was no particular problem for copper wirings having a semiconductor wiring width of up to 0.18 μm.
Nevertheless, with ultra fine wiring where the copper wiring width is 0.13 μm or less; for instance, 90 nm or 65 nm, and the aspect ratio exceeds 8, the thickness of the seed layer would become an ultra thin film of 100 nm or less, and, when forming a seed layer with a 6N purity copper target, there was a problem in that coagulation would occur and a favorable seed layer could not be formed. Thus, proposals of containing 0.5 to 4.0 wt % of Al or Sn have been made to overcome the problem.
As described above, the uniformity of the foundation layer is important, and, when the foundation layer becomes coagulated, it is not possible to form a uniform film upon forming a copper film via electroplating. For example, defects such as voids, hillocks, and disconnections are formed upon wiring.
Even if defects such as voids described above are not formed, since an uneven electrodeposited texture of copper will be formed in this portion, there is a problem in that the electromigration resistance will deteriorate.
In order to overcome this problem, it is important to form a stable and uniform seed layer upon performing copper electroplating, and a sputtering target optimal in forming a seed layer having superior sputter deposition characteristics is required. Thus, the foregoing inclusion of 0.5 to 4.0 wt % of Al or Sn for preventing coagulation was extremely effective for this purpose.
Nevertheless, it has been discovered that there is a drawback of the sheet resistance of the sputtered film becoming too large. There is a problem in that the sheet resistance will become too large depending on the use, and it is not necessarily effective when focusing on the purpose; that is, the conductivity.
In light of the above, attempts have been made for reducing the sheet resistance by forming a sputtered film, and subjecting this to heat treatment so as to form a deposit. Nevertheless, Al and the like have a high solid solubility limit, it was substantially difficult to form a deposit and reduce the sheet resistance. Further, subjecting the film to heat treatment raised additional problems of complicating the process and affecting the device with heat.
Moreover, although proposals have been made for reducing the resistance of the copper wiring by dispersing Al on the wiring film surface via heat treatment and improving the oxidation resistance (for example, c.f. Japanese Patent Laid-Open Publication No. H6-177117), when this kind of processing is performed on the seed layer, an Al oxide film is formed on the seed layer, and this is inappropriate since the conductivity of the electroplating base layer will decrease.
Heretofore, as the copper wiring material, a method has been proposed of adding certain elements to copper in order to improve the electromigration (EM) resistance, corrosion resistance, bond strength and so on (for example, c.f. Japanese Patent Laid-Open Publication No. H5-311424 and Japanese Patent Laid-Open Publication No. H1-248538). Further, also proposed is a pure copper target or a target in which 0.04 to 0.15 wt % of Ti is added thereto (for example, c.f. Japanese Patent Laid-Open Publication No. H10-60633).
And, in the foregoing proposals, rapid cooling for the uniform dispersion of the added elements, or continuous casting for preventing the segregation of added elements in ingots, shrinkage cavity during casting, and coarsening of crystal grain in ingots are being proposed.
Nevertheless, although there is an advantage in that the specific resistance is low with high purity copper or when minute amounts of metal are added thereto, these cannot necessarily be considered favorable materials since there is the problem of electromigration and the problem of oxidation resistance during the process.
In particular, since the aspect ratio is becoming even higher in recent years (aspect ratio of 4 or higher), sufficient electromigration resistance and oxidation resistance are being sought.
In light of the above, a proposal has been made for adding Al or Sn (or other various elements such as Ti or Zr) to copper to obtain a copper alloy to be used as the target for a wiring material (for example, c.f. Japanese Patent Laid-Open Publication No. H10-60633). Nevertheless, this is for improving the EM resistance, SM resistance or oxidation resistance without hindering the low resistance characteristics of copper, and could not be used for forming a seed layer in an ultra fine copper wiring process by performing the copper electroplating described above (for example, c.f. Japanese Patent Laid-Open Publication No. H6-177117).
Further, there is also a proposal stating that 0.5 wt % of Sn is effective in reducing the grain boundary diffusion of Cu and improving the EM characteristics (for example, c.f. [Electromigration and diffusion in pure Cu and Cu(Sn) alloy, Mat. Res. Soc. Symp. Proc. Vol. 427, 1996], Materials Research Society, written by C. H. Hu, K. L. Lee, D. GupTa, and P. Blauner (IBM)). Nevertheless, this does not resolve the coagulation problem with the seed layer on the barrier layer formed with the likes of Ta or TaN.
Accordingly, with conventional technology, a copper alloy which allows the formation of a seed layer having a high conductivity and being stable and uniform during copper electroplating has not been obtained and, in particular, a technology for manufacturing a semiconductor element wiring was not necessarily sufficient.